There were five named solar minima in the last millennium – the Oort, Wolf, Spörer, Maunder and Dalton minima. At least the last four were all associated with cold climates. The astrophysics community has elected to name the current period of low solar activity the Eddy Minimum. John A. Eddy was an American astronomer who compiled data demonstrating the periods of low solar activity prior to the Dalton Minimum. The Eddy Minimum will include at least Solar Cycles 24 and 25, and could continue until late in the 21st Century.

Benjamin Franklin was the first to suggest that volcanic eruptions might affect climate, in a 1784 communication to the Literary and Philosophical Association of Manchester:

“During several of the summer months of 1783, when the effect of the sun’s rays to heat the earth in these northern regions should have been greatest, there existed a constant fog over all of Europe, and a great part of North America. This fog was of a permanent nature; it was dry, and the rays of the sun seemed to have little effect toward dissipating it, as they easily do to a moist fog, arising from water. They were indeed rendered so faint in passing through it, that when collected in the focus of a burning glass, they would scarce kindle brown paper. Of course, their summer effect in heating the earth was exceedingly diminished.Hence the surface was early frozen.

Hence the first snows remained on it unmelted, and received continual additions.

Hence the air was more chilled, and the winds more severely cold.

Hence perhaps the winter of 1783-84 was more severe, than any that had happened for many years.

Benjamin Franklin was referring to the Laki eruption in Iceland of 1783. This was accompanied by an abnormally hot summer in Europe and then an exceptionally cold winter in Europe, the United States and Japan. In the United States, Charleston Harbour froze and the Mississippi River froze at New Orleans between 13th and 19th February, 1784. When this logjam of ice broke up, ships encountered ice flows in the Gulf of Mexico 100 km south of the delta. The famine in Iceland caused by the Laki eruption killed 24 percent of the population.

In the second half of the Modern Warm Period, when solar activity was at its highest for 8,000 years, there was one volcanic eruption large enough to affect climate. This was the eruption of Mt Pinatubo in the Philippines starting on 15th June, 1991. It ejected 10 cubic kilometres of magma and 20 million tonnes of sulphur dioxide. The aerosols it injected into the stratosphere lowered the global temperature by 0.5°C in 1992, with a peak effect of 0.7°C. The impact on agriculture though was not significant. Some wheat farmers in the northern part of the Canadian wheat belt found that the cool growing conditions didn’t allow their crops to mature in time before winter set in. They resorted to using Roundup to make hay from their standing wheat crops.

When major eruptions are overprinted on a period of cold climate, the effect is far more severe. As John A. Eddy said in reference to the Mount Tambora eruption of 10th April, 1815, “The unusual summer of 1816 is commonly attributed to the increase in atmospheric turbidity that followed the eruption of Mount Tambora. The awesome eruption occurred, in fact, during a span of several decades of colder climate that had interrupted the gradual global warming that followed seventeenth century extrema of the Little Ice Age. These background trends may well explain a particularly severe seasonal response in 1816 to a short-term injection of volcanic dust.”

The impact on climate and agriculture of the Mount Tambora eruption on the North-eastern United States is reasonably well documented. The current great grain producing area of the United States is 1,100 kilometres to the west. Nevertheless, what happened in the north-eastern states two hundred years ago is a good proxy for how the Corn Belt will respond to a major volcanic eruption during a climatic cool period. Visitors to the mid-western states in that period noted mid-summer frosts up to the mid-19th Century.

William R. Baron compiled the weather record of the north-eastern United States in his paper contained in the book “The Year Without a Summer? World Climate in 1816”:

“The year began, at least in Phillipstown, Massachusetts, with enough snow on the ground for sleighing. All over New England, January was a snowy, stormy month until the very end when a sudden thaw caused localised flooding such as the one reported by Isaiah Thomas at Worcester, Massachusetts on 23rd January where some mill dams were carried off and some items stored in a warehouse were destroyed. According to among others, Leonard Hill of East Bridgewater, Massachusetts, February was a mild and pleasant month with only three snows reported. By the beginning of March there was little deep snow anywhere with the exception of most of northern New England. Early March was clear and cold, and was followed by a series of three snow storms around mid-month that produced a few days of sleighing but soon melted. On 28th and 30th March, warm air returned producing thunder and lightning as reported by Elijah Kellogg at Portland, Maine and Thomas at Worcester.

April quickly turned cold again with frequent frosts and some snow. However, by 14th April, there was little snow left at Hallowell, Maine. By 19th April, Alexander Miller of Wallingford, Vermont had begun to plough his fields; Stephen Longfellow of Gorham, Maine was already planting wheat; and Theodore Lincoln of Dennysville (in far down-east Maine) was reporting ice-out on the local streams – a sure sign of coming spring. At the end of the month, Joshua Lane of Sanbornton, New Hampshire already was reporting the start of a drought that would later plague all of northern New England.

In early May, farmers throughout the region completed planting their major crop, corn. By mid-month, the weather had become “backward” with a “heavy black frost’ that froze the ground to at least one-half inch reported on 15th May as far south as Trenton, New Jersey. Miller, at Wallingford, Vermont, reported snow on 14, 17 and 29 May while Lane, over at Sanbornton, saw a large frost on 29th May, and ended the month with further complaints about the continuing drought. B.F. Robbins, visiting Concord, New Hampshire noted that May ended with two days of “remarkable cold” that froze the ground “to near an inch.”

June is the month most remembered for its outbreak of cold weather. On 4th June, there were frosts at Wallingford, Vermont and Norfolk, Connecticut. By 5th June, the cold front was reported over most of northern New England. On 6th June, snow was reported at Albany, New York and Dennysville, Maine, and there were killing frosts at Fairfield, Connecticut. 7th June brought reports of severe killing frosts from across the region, and as far south as Trenton, New Jersey.

Typical of comments by diarists concerning this day are those by George W. Featherstonehaugh of Albany, New York, who wrote that the frost killed most of the fruit, as many apple trees were then just finishing blossoming. Leaves on most of the trees were “blasted” by the cold. Corn and vegetable crops were injured. He also feared that many of the sheep that had just been sheared might die of cold.

Cold weather continued through the night of 10th June. By the end of the month most observers were reporting the return of warm weather, but by then most crops were either killed or “backward” and stunted in their growth. In northern New England, those crops that survived the frosts were hit by what was now a very serious drought, greatly reducing the production of one of the area’s primary crops, hay.

In early July there was another outbreak of cold weather in northern New England. On 5th July, at Gorham, Maine, there was a very hard frost. Benjamin Kimball of Concord, New Hampshire and Thomas Robbins of Norfolk, Connecticut reported hard frost on 7th July. There was frost on 8th July at Portland, Maine and on the following day at Sanbornton, New Hampshire. Thereafter the cold held off for the remainder of the month. Dry conditions, generally reported earlier in northern areas, persisted throughout the entire month.

Frosts returned on the morning of 21st August, being reported at York and Portland, Maine and Wallingford, Vermont. By 22nd August hard frosts were noted all over the region and as far south as Trenton where buckwheat crops were killed. Thomas, at Worcester, Massachusetts, reported that these frosts “cut off Indian corn in many places”, while others such as Hill at East Bridgewater, Massachusetts observed that frosts did little or no damage.

The frosts continued into September. In northern New England there were frosts on 10th and 11th September and throughout New England during 25th to 27th September. On 28th September, there was a killing frost throughout the region extending as far south as Trenton. It killed any vegetation that had somehow survived to that date. The drought in northern New England was finally broken by rains in the last week of the month.

The remainder of autumn was very mild with very few snowfalls or storms. December was also mild, until the last 10 days or so, when it turned cold enough to freeze the harbour at Beverley, Massachusetts. The year ended as it began, with enough snow on the ground at Phillipstown, Massachusetts to use a sleigh.”

1816 had an extremely short growing season. In southern Maine, it had averaged 140 days up until then but plunged to 70 days in 1816. Consequently farmers experienced an almost total failure of major crops. There was a fair yield of winter grain, but other crops such as corn and hay failed leading to the loss of many sheep and cattle for lack of feed during the following winter. As a result, 1816 has come down to as the “cold year”, “the famine year” and ‘eighteen hundred and froze to death”. For eastern Massachusetts, 1816 is the only year in which young corn was killed in the spring after it had sprouted and in which corn that survived replanting was killed in the autumn, before it could reach maturity. Under these circumstances, it is safe to assume that in most places in New England corn crops were an almost total failure. The story for 1816 is the same for New Hampshire and Maine. There were a number of periods in which corn crops were hit by late spring or early autumn frosts. Particularly difficult periods include: 1793-96, 1812-17, and 1835-36.

The effect of the Mount Tambora eruption is also well documented in Europe. From 1813 to 1815, harvests were generally lower than expected. However, 1816 was a year of calamity for most of the continent. Spring saw heavy rains which were followed by snow in June and July that caused widespread harvest failures. Wheat yields in France, England and Ireland were at least 75 percent lower than at the beginning of that decade. Wholesale wheat and rye prices responded by roughly doubling in 1817 across the continent. The area affected the most was southern Germany where prices increased by three hundred percent by the period May to June of 1817. In Germany and Switzerland, people resorted to eating rats, cats, grass and straw as well as their own horses and watchdogs. This was the last great subsistence crisis of western civilisation.

The climate of Switzerland in 1816 inspired Mary Shelley to write the novel Frankenstein and her host, Lord Byron, to write his poem Darkness in July of that year. The first nine lines of the poem give a sense of what the days were like:

I had a dream, which was not all a dream.
The bright sun was extinguish’d, and the stars
Did wander darkling in the eternal space,
Rayless, and pathless, and the icy earth
Swung blind and blackening in the moonless air;
Morn came and went–and came, and brought no day,
And men forgot their passions in the dread
Of this their desolation; and all hearts
Were chill’d into a selfish prayer for light

With a solar activity now falling away and return to cold climate conditions imminent, it would be a useful exercise to calculate what would happen to American crop yields using the year-by-year climate conditions of the first half of the 19th Century. This would give an indication of the size of the problem. It could be that grain production might fall 60 percent from what it is now in the event of a major volcanic eruption during the Eddy Minimum. No American need starve if they were happy to live on a diet that was mostly corn and soybeans. The price of meat would skyrocket and a large portion of the national herd of lot-fed cattle and pigs would be slaughtered to avoid the cost of feeding them. Grain production in Canada in an 1816-type year would be wiped out completely. An indication of what would happen to food pricing and availability is the price response of oats in the north-eastern United States in 1816, which rose from 12 cents a bushel to 92 cents a bushel.

A repeat of the climate experience of 1816 in the world’s temperate region grain belts would most likely result in almost all of the grain exporting countries ceasing exports in order to conserve grain for domestic consumption. The effect on countries currently importing grain would go beyond calamity to catastrophe. The resultant mass starvation event would become the largest event in human history.

Current grain stocks carried by countries around the world assume that tomorrow will be much the same as today. As at year-end 2012, total world grain stocks were estimated to have been 328 million tonnes, which equates to 21% of annual demand. The days of the continuous benign climate of the second half of the 20th Century, due to the highest solar activity for the last 8,000 years, are now past. Perhaps continuing cooling over the rest of this decade will suggest to some that it would be prudent to plan on the basis that the climate for grain growing will continue to get worse, before there is another major volcanic eruption. Absence of planning could be considered as a suicidal tendency. Major volcanic eruptions occur about every 45 years on average. At the present, in the year 2013, with the oceans warmer than they have been for 800 years, the chance of a Mount Tambora-like eruption causing another mass famine is very slight. The world will be much cooler by 2020 though, and with an average period between eruptions of 45 years the chance of any individual year witnessing a mass famine event after 2020 will be about two percent. The cumulative chance rises to near 40 percent for the period 2020 to 2040. The world may dodge that bullet. Or it may not. Cold-driven reductions in grain supply will be quite distressing even to those who are fully prepared. The unprepared will become quite dead.